Compounding of buna s with blown oils



Patented June 25,1946 v I 7 2,402,909 UNITED STATES PATENT OFFICE COMPOUNDING F BUNA S WITH BLOWN OILS No Drawing. Application February 20, 1943, Serial No. 476,629

v 8 Claims. (Cl. 260-23) 1 2 This invention relates to improvements in the ,and China-wood oil are useful preferably only compounding of the synthetic rubber or rubbery in the blown state. It will therefore be undercopolymer of butadiene-L3 and styrene known stood that the oil capable of producing a factice, as Buna S, and particularly to the plasticization or oil capable of producing a factice on vulcanthereof so as to impart to the product specific 5 ization with sulfur, as used in the within specidesirable properties. flcation and claims is intended to include those Buna S, which is a linear and cross-linked covegetable or fish oils either thus generically despolymer resulting from the catalytic polymcrizaignated, or individually and specifically desigtion of an emulsion of butadiene and styrene, nated, which are capable of being vulcanized while superiortonatural rubberinsome respects, with .sulfur in either the fluid, blown, gelled has been found to be inferior iii others, and parblown or unblown state, or the blown state alone, ticularly in respect to processing dimculties, and and to exclude all other oils. the ability to form a product which has the de- In order to obtain the maximum of the foresirable properties of extensibility and elasticity, going desirable properties I have found that the resiliency (i. e., low hysteresis), low heat buildmost satisfactory form of oil is one which has up, good tack or adhesion and resistance to exbeen air or oxygen blown to an extent where it tremes of temperature. has a viscosity of from about 10 to about In particular I have found that the ability to poises at normal room temperature or about 72 satisfactorily compound Buna S and to enable R, the blowing preferably having been carried out it to be processed by conventional rubber equip- 20 at a low temperature such as about to about ment and technique and to form products hav- 70 C. Although I may with substantially equal ing the aforementioned desirable properties, is effect use an oil blown to a temperature as high to a large extent dependent upon the initial plasas 180 C., the low temperature blown oil is prefticization treatment thereof, and particularly in erable since it is more uniform, that is, it conthe nature of the plasticizing agent, conventional 5 tains less unblown oil and break-down products, natural rubber plasticlzing agents having been and produces better tensile and elastic properfound to be unsatisfactory. ties. on the other hand I may use the oil blown It is therefore an object of this invention to to the gelled state, that is, blown directly to a gel compound Buna S and-particularly to plasticize or first blown and then heat gelled, or use it in it by means of novel plasticizing material so as to so the fluid condition in viscosities ranging from enable the production of more rubber-like Buna S about 2 to about 100 poises at 72 0., or even in products as evidenced by greater liveliness and an entirely unblown condition, if it is a factice lower internal friction. forming oil in such condition, dependent on the In accordance with the present invention I nature of the ultimate product desired or the use have found that avegetable or fish oil capable or purpose thereof. It will therefore be underof producing a factice and which is compatible stood that although I may use either unblown, with and soluble in Buna S and which permits a fluid blown, or gelled blown oils of the factice co-vulcanization of the solution of the oil in the forming type for the plasticization of Buna S, Buna S by means of sulphur, forms a good plaseach of these oils or the forms of the particular ticizing agent therefor. Such plasticization per- 40 oil produced as previously set forth is not necesmits the Buna S to be readily compounded and sarily equivalent in the character of the result milled by means of conventional rubber rolling produced, and with the various oils and forms mills or internal type mixers, and enables the varyingproportions to accomplish related results production of vulcanized products of good physmay be required, although all forms show marked ical properties such as excellent tensile strength, improvement over standard natural rubber plasplasticity, and heat build-up properties, high ticizers in producing Buna S stocks having low elongation, low modulus, good rebound, tack and heat build-up and low hysteresis loss under meelectrical properties, much improved resistance chanical stress.

to heat embrittlement, and with little if any Thus I have found that for the best products, effect on the known good abrasion resistance of such as those suitable for use in the carcass of Buna'S. a tire it is preferable to use from about 10 to The oils which I have found to be useful may about 20 parts by weight on 100 parts of Buna S, be vegetable or fish oils of the drying, semi-dryof the oil which has been blown at a temperature ing or non-drying type and includes such oils as of from about 25 to about 70 C. and having a linseed, soya bean, hempseed, oiticica, Perilla, viscosity of from about 10 to about 20 poises menhaden, pilchard and the like which are caat normal room temperature or about 72 F. pable of forming a factice on vulcanization with Such proportions give an unvulcanized compound sulfur. Althoughthe foregoing specifically enuof the highest tack required for cloth lamination merated and other oils are useful in the blown and for permitting adhesion by contact of plies or unblown state, certain oils such as castor oil such 'as in the building up of a tire carcass, and

permits frictioning or skim coating by means of conventional calendering apparatus. Such formulation also permits the production of thin wall extruded products and permits better spreading in calendering operations. Tread type stocks may use from about to about parts of the 10 to 20 poise at 72 F. oil to produce satisfactory Buna S: carbon black stocks. 1

- As previously indicated, oils of greater or lesser viscosity than the foregoing preferred range are useful although for non-equivalent purposes and in varying character of the product. Thus as the viscosity of the oil increases beyond about 20 to 25, poises and approaches the gel stage, the tack drops 011', although good tack is still obtainable even with the fully gelled oil. On the other hand oil of lower viscosity, such as the unblown or mildly blown oil may be used in the proportion of from about 5to about 10 parts or Runs. 8 in the compounding of stocks requiring moderate improvement in plasticity and lower tack, such as in thick extrusion products, mechanical rubber goods, and certain tire tread compounds.

In a modified method of compounding Buna S I may replace about one-half of the indicated amount of oil, particularly the fluid blown form by rosin, with the result that slightly higher tensiles but lower elongations are obtained in the vulcanized product than when using the full amount of oil alone. In this respect it is important to point out, however, that rosin alone in any proportion is not useful as a plasticizer for Buns. S.

The processing or compounding may be carried out by means of conventional equipment such as a rubber mill or internal type mixer such as a Banbury mixer, and is preferably conducted with the rolls or mixer maintained cold for best results. For examplein a mill mixing operation the Buna S is preferably first broken down in a tight cold mill, the plasticizer then added in small increments, and thereafter the pigments or blacks are added. Toward the end of the mixing schedule the sulphur and accelerators may be added, followed by remilling after aging. with the result that the Buna S compounded with my plasticizer produces a stock of greatly reduced nerve.

It is important to point out that although the plasticizers of this invention are characterized as being of the factice producing type, the manner of their use, function and resultant effect is distinct from the well known use of a factice in the compounding of natural rubber, such former use having been in the addition of the vulcanized oil or factice to the rubber as a filler or adulterant. In my process the oil is added before vulcanization, and for the purpose of acting as the essential plasticizing agent, and only thereafter is the oil co-vulcanized with the Buna S in an otherwise cured compound, greatly improving'the plasticity and permitting better extrusion and calendaring of the blends. This leads to easier processing without sacrifice of quality. The low heat buildup imparted to the Buna S compounds with the use of my plasticizers is especially of value in tire carcass compounding.

The advantages and results obtainable by the use of my plasticizers in the compounding of Buns. S in typical compounds is shown by the fol-- lowing comparative tables, which should be considered as illustrative and not for the purpose of limiting the scope of my invention. Thus for the purpose of better comparison, in all of the following examples the indicated plasticizer used was a fluid low temperature air blown linseed oil having a viscosity oi? from about 10 to about poises at 72 F. All proportions are shown in parts by weight.

Table I Compound No.

5 5 5 l. 5 I. 5 5 l. 5 l. 5 6 6 10 a EEQe .32 a sa as a use The foregoing table illustrates that the addition of my plasticizer to a Buna S-Channel Black compound results in lower moduli, higher elongations, and lower durometer hardness values. The tensile values are of the same order regardless of the amount of plasticizer added up to about 20 parts on one hundred Buna S.

The addition 01' 20 parts of the same plasticizer to a semi-reinforcing channel black stock was tested for its effect on the phenomenon of overcuring. At the end of a 19 hour cure at 287 F. the tensile, elongation and hardness had increased compared to the one hour cure. The modulus at 300% elongation had remained the same. This blend showed no signs of over-curing, other than hardness, over the long curing time.

The comparative effect of the use of a modified form of my plasticizers composed oi 50% by weight of rosin and 50% by weight of a blown oil plasticizer similar to that of the foregoing examples indicates that slightly higher tensile and lower elongation result thereby, as shown by the generally conventional rubber compound, with a following mparative results:

apparent uniform rapidity of vulcanization as distinguished from the relatively slow vulcanization of a factice per se. to result in a compound of improved processing qualities and in mutual beneficial modification in the final vulcanized product.

One of the particular advantages arising out ofuse of my plasticizers is that they may be used in greater amounts than has been possible heretofore in the attempt to plasticize Buna S with 10 commercial natural rubber plasticizers, without reducing the physical properties of cured blends to the extent which results when using equal amounts of such commercial plasticizers, the ad- Table II Modulmat w Three blends, one with medium sulphur and dition greatly reducing the "nerve of the un- 1| two with high sulphur, were aged in a Geer oven and oxygen bomb. Using the same plasticizer as in the foregoing examples the oxygen bomb aging showed little or no effect on the tensile and elongation values. On the other hand a conventional and commercial coal tar hydrocarbon oil rubber plasticizer tested under the same conditions showed reduced tensile and elongation values. Air oven aging resulted in slightly increased tensile values using my plasticizer with decreased elongation values. As compared to this the commercial rubber plasticizer showed greater loss in elongation and tensile values.-

The following Table III illustrates that the addition of my plasticizer to a channel black tread type stock in compounds Nos. 7 and 8, similar to those of Nos. 3 and 4 of Table I, resulted in good rebound properties which increased with increase in temperature. The heat build-up was low for this type of compound. Compared to the use of a commercial type of coal tar hydrocarbon oil rubber plasticizer as typified by compound No. 9, the use of my plasticizer shows low heat build-up and less distortion of sample slugs during the test operation. Whereas the Buna S compounded with the commercial rubber plasticizer became distorted to such an extent that it would not remain in the test machine, the test slug of the compound embodying my plasticizer remained in the test equipment under a 192 pound load. When it is considered that a hard channel black was used in this series of tests, the low heat build-up of the stock utilizing my plasticizer is noteworthy. ,Thls comparative test data is shown in the following Table III.

Table III Compound No.

Buna B 100 100 100 Channel Black. 50 50 50 Zinc oxide 5 5 5 Sulphur l. 5 1. 5 l. 5 Benzothiazol disulphide- 1.0 l. 1. 0 Di-ortho-tolylguanidine 6 5 Plasticizer i0 Commercial rubber plasticizer 60 MIN. CURE AT 287 F.

Per cent rebound at 72 F 40. 7 36. 9 40. 2 Per cent rebound at 212 F..- 49. l 42. 8 39. 4 Per cent increase at 212 F +20. 6 +16. 0 2. 0

GOQDRICH FLEXOMETER HEAT BUILD-UP [Conditions: .125 inch stroke-148 lb. load] Initial dynamic compression... 2M 242. 419 Final dynamic compression 310 350 575 Dynamic compression drift. 76 108 156 Initial temperature, C 28. 8 29. 0 32. 7 Final temperature, C. 87.6 89.6 136.4 Temperature increase, 0.. 58. 8 60. 8 103. 7 Time of run, mins 30 30 30 [Conditions: .125 inch stroke-192 lb. load] Initial dynamic compression 295 335 460 Final dynamic compression 400 475 600 Dynamic compression drift. 105 140 140 Initial temperature, 0. 27. 4 26.9 35. 6 Final temperature. C 101. 8 112.0 131. 5 Temperature increase, 74. 4 85. 1 95.9 Time of run, mins 30 30 I 7 I Sample slid out of machine.

The foregoing data on heat build-up was substantiated and expanded by a series of tests incorporating increasing quantities (5 to parts) of the same plasticizer as used in all of the within examples (10 to 20 poise low temperature blown linseed oil) in a carbon black tread stock similar to compound-Nos. land 2: of Table III, these tests showing that the hysteresis loss remained practically constant through the series, as against all the well known plasticizers for natural rubber which increase hysteresis'loss as more is added. This characteristic makes it possible to produce soft, tacky, easy extruding tread stocks which do not harden in use to a brittle point, and to do this while maintaining resilience and low heat build-up properties.

Samples of Buna S containing 50 parts of semi-reinforcing channel black on parts of Buna S and plasticized with six parts by weight of I my aforesaid plasticizer, or my 50 per cent rosin ralastlcizer, remained flexible after four days at 5 C. The electrical properties of Buna 8 compounded with my plasticizer have been found to becomparable to those exhibited by the use of commercial rubberplasticizers. Tear resistance which is greatly influenced by the degree of black dispersions has been found to be high in Buna S black compounds, compounded with my plasticizer and excellent results have been obtained on compounds of the carcass A test developedby one of the major carbon black suppliers determines the number of seconds which elapse between the contact of a hot surface and the breaking of a sample cut from a test sheet. Whether the test shows high temperature tensile, elongation, or tear, the fact is that many Buna S compounds break in a few seconds. A carcass compound similar to the foregoing examples containing 10 parts of the plasticizer onlOO parts of Buna S lasted 187 seconds. A similar compound without the use of my plasticizer broke in 4 seconds.

I claim as my invention: I

1. A compound of the rubbery copolymer of butadiene-Lli and styrene containing a blown oil capable of producing a factice on vulcanization with sulphur as the plasticizer therefor, said oil having a viscosity of from about 10 to about 20 poises at 72 F. and being in the proportion of from about 5% to about 25% by weight of the copolymer.

2. A compound of the rubbery copolymer of butadiene-1,3 and styrene containing a blown oil capable of producing a factice on vulcanization with sulphur as the plasticizer therefor, said oil having a viscosity of from about 10 to about 20 poises at 72 F. and being in the proportion of from about 10% to about 20% by weight of the copolymer. 1

3. A compound of the rubbery copolymer of butadiene-1,3 and styrene containing a plasticizer therefor composed of approximately equal parts by weight of rosin and a'blown oil capable of producing a factice, the oil having a viscosity of from about 10 to about 20 poises at 72 F., the plasticizer being in the proportion of from about 5% to about 25% by weight of the copolymer.

agcoaooa 7 about 5% to about 25%:byweisht'ot a-mixture composed oi approximately equal parts by weight of rosin and a blown oilcapable of producing a iactice having a viscosity of irom about 10 to about 20 poises at 72 1''.

6. A compound'of the rubbery copoiymerjoi butadiene-1,3 'and styrenecontaining blown linseed oil as a plasticizer. therefor, said linseed oil havinga viscosity'ohfrom about 10 to about 20 poises at 72 F.; afidibeing in the proportion 01 from about 5% to about 25% by weight of the copoiymer. p

'- 73A 'con'ipounwoi -tbei rubbery copolymer of butadIene-LB and styrene containing blown lin- -seed0i1fas a plasticizer thereior,,said linseed-o having -a- -viscosity of from about 10 to about 20 pulses at 72 -F., and being in the proportion oi copolymer. 

